Clearance patterns of the isolated guinea pig duodenum.

To determine what role duodenal clearance plays in the resistance that the duodenum generates to gastric emptying, duodenal output in vitro was assessed under a variety of preload and after-load conditions. In the presence of an outflow resistance, duodenal output occurred in pulses related to contractions of the duodenum. Stroke volume (incremental output during a single contraction) and cumulative output increased both with the degree of duodenal filling and with pharmacological stimulation. Cumulative output decreased as outflow resistance was increased from 0.5 to 5.0 cm water pressure; there was no further decrease on raising outflow resistance to 10.0 cm water pressure. Output volume was similar from the proximal and the distal duodenum. The stroke volume produced by individual duodenal contractions remained stable over a wide range of load conditions. The threshold volume and the luminal pressure at which output from the duodenum started were higher with retrograde perfusion of the duodenum than with antegrade perfusion. Also, the contraction rate of the duodenum decreased markedly with retrograde perfusion, and the powerful contractions occurring in this setting often involved the entire segment simultaneously. The findings suggest that the duodenum responds to load and to flow conditions so that luminal clearance is maintained; clearance is achieved by both antegrade and retrograde displacement of contents from the lumen at the contraction site.